The present invention relates to engine thermal management, and more particularly to engine thermal management where temperatures are precisely controlled and flow rates of the coolant are reduced.
Conventionally, in a vehicle engine, a cooling circuit employing a radiator is used to remove excess heat from the engine, maintain a constant operating temperature, increase the temperature in a cold engine quickly, and heat the passenger compartment. The cooling circuit uses a coolant, which is typically a mixture of water and anti-freeze. The cooling circuit includes a water pump that is powered via the crankshaft of the engine, and forces the water through the cooling circuit components. The flow path typically consists of the coolant flowing from the water pump through the engine block passages, then through the engine head passages, then out of the engine and through hoses to the radiator, and from the radiator through a hose back to the water pump. A portion of the coolant may also be routed through a heater core when there is heat demand in the passenger compartment of the vehicle, or through a radiator bypass when the coolant temperature is below its desired operating temperature. The volume of coolant flow is kept high enough to assure that all of the engine components are cooled sufficiently under extreme operating conditions. With this high volume of coolant flow, the coolant temperature to the engine is generally low, with a generally constant coolant temperature for coolant leaving the engine. This high volume makes assuring that all of the engine components remain below their critical metal temperatures relatively easy. However, these conventional engine cooling systems, while straight forward and relatively easy to implement, are not very good at providing optimum cooling for the particular engine and vehicle operating conditionsxe2x80x94particularly since the water pump speed is strictly a function of the engine speed (not the amount of cooling needed by the system), and the routing of the coolant to the various components of the system is limited. Moreover, the system tends to consume more power to operate than is desirable.
In order to obtain more precise cooling for engine, advanced engine thermal management systems have been developed. A more advanced system may be, for example, a system and method as described in U.S. Pat. No. 6,374,780, assigned to the assignee of this application, and incorporated herein by reference. These newer systems take into account addition factors that influence both what the desired coolant temperature is and how it is achieved. Such a system might include a water pump (with variable speed control) that pumps water into the engine block passages, then through the engine head passages and out into a flow control valve. The flow control valve then selectively distributes the flow between the radiator, a bypass line, the heater core, and a degas container. With the improved efficiency of heat transfer and more precise control over the engine cooling, these advanced systems can operate with a reduced flow rate of coolant. This allows for minimizing the pumping power used and also maintains higher metal temperatures during the majority of the driving cycle of the vehicle (mainly at low engine power conditions), which allows for improved engine operation. However, under high engine power conditions, the lower heat transfer coefficients due to the reduced coolant flow increase the potential for excessive metal temperatures at certain locations in the engine. In particular, as the coolant flow rate is reduced, the coolant temperature rise across the engine (from where the coolant enters the engine to where it exits) increases. And, since a dominant parameter in controlling the metal temperature is the local coolant temperature, excessive metal temperatures at certain locations can occur.
In particular, these advanced systems also direct the flow of coolant in the same direction through the engine as the conventional engine cooling systemsxe2x80x94that is, the water pump sends the coolant into the engine block, and then from the block the coolant flows to the head, and then is returned to the radiator for cooling. The reduced coolant flow does not adversely effect the vehicle radiator heat dissipation since it is controlled more by the air flowing through the radiator than by the coolant flow rates. However, due to the significant temperature rise of the coolant across the engine, this can create a situation where the critical metal temperature for certain portions of the engine head are exceeded.
Thus, it is desirable to minimize the coolant flow rates, and accordingly cooling power requirements, in an advanced engine thermal management system, while avoiding excessive critical metal temperatures in the engine.
In its embodiments, the present invention contemplates an engine thermal management system for an engine having head, with a coolant inlet and head passages connected to the inlet, and a block, with a coolant outlet and block passages connected between the head passages and the outlet. The engine thermal management system has a water pump having a pump outlet adapted to operatively engage the coolant inlet and pump a coolant thereto, and a pump inlet; and a multi-port valve having a valve inlet adapted to operatively engage the coolant outlet of the block, a first valve outlet selectively engagable with the valve inlet, and a second valve outlet selectively engagable with the valve inlet. A radiator operatively engages the first valve outlet and the pump inlet, and a bypass operatively engages the second valve outlet and the pump inlet. The engine thermal management system also includes a controller operatively engaging the valve to control the selective engagement of the valve inlet with the first valve outlet and the second valve outlet.
The present invention further contemplates a method of controlling the cooling of an engine, having a block and a head, in a vehicle comprising the steps of: pumping coolant into a coolant inlet in the head of the engine; routing the coolant through coolant passages in the head; routing coolant from the coolant passages in the head to coolant passages in the block of the engine; routing the coolant from the coolant passages in the block to a coolant outlet in the block; routing the coolant from the coolant outlet in the block to an inlet of a multi-port valve; selectively routing portions of the coolant from the inlet of the valve to at least one of a radiator, a heater core, a bypass, and a degas container; and electronically controlling the pumping of the coolant and the routing through the multi-port valve based on engine operating conditions.
An advantage of the present invention is that coolant flow rates in the engine cooling circuit are reduced while still being able to maintain the desired engine operating temperature. This allows for a reduction in the power consumed by the cooling.
A further advantage of the present invention is that, while the coolant flow rates are reduced, the critical metal temperatures in the engine head are maintained at acceptable levels.